This invention relates to a positive photosensitive polymer composition which is suited for use in the formation of pattern of insulation film, passivation film, .alpha.-ray shielding film, optical waveguide and the like, which are employed in various electronic parts. This invention relates also to a method of forming a pattern by making use of the aforementioned positive photosensitive polymer composition, and to electronic parts provided with a pattern of the aforementioned positive photosensitive polymer composition as an insulation member or as a passivation member.
In the ordinary semiconductor device having semiconductor elements formed on the surface of its substrate, the surface of substrate is generally covered with a protective film called a passivation film for the purpose of protecting the semiconductor elements from any influence of the external environment thereby improving the reliability of the semiconductor device. As a material for this passivation film, a polyimide resin is extensively employed in view of its excellent properties such as electric properties (e.g. insulating characteristics), radiation resistance, environmental stability and heat resistance. Furthermore, this polyimide resin is widely employed in a semiconductor device as an .alpha.-ray shielding film, or as an interlayer insulating film for a multilayered wiring structure or for a multilayered element structure (a multichip module).
This polyimide resin can be easily formed into a film from polyamic acid which is a precursor for the polyimide. Namely, a varnish of polyamic acid is coated on the surface of a predetermined substrate and then the coated layer is heated to form a film of polyamic acid, which is then heat-treated at a high temperature thereby to cause a cyclodehydration reaction of the polyamic acid to take place, thus curing the polyamic acid film and forming a polyimide film. It is possible, with the employment of this method, to easily form a film of polyimide in spite of the fact that polyimide can be hardly worked since it is not or hardly soluble to most of organic solvents and is high in softening point. Therefore, the aforementioned method has been widely adopted in the formation of polyimide film.
Meanwhile, in the manufacture of a semiconductor device, various workings, for example, for forming a through-hole in a multilayered wiring structure or for forming a pad for effecting an electric connection with an external lead are required. In order to carry out these workings, a polyimide film formed as a passivation film or an interlayer insulating film as explained above is required to be patterned thereby to form holes or grooves of predetermined patterns. Generally, the patterning of polyimide film is performed by making use of PEP (photo-engraving process) using a photoresist. Namely, after a polyimide film is formed on the surface of a semiconductor substrate bearing a semiconductor element thereon in the method as mentioned above, a photoresist film is further formed on the surface of the polyimide film and then subjected to a light exposure process followed by a development process thereby forming a resist pattern. Then, the underlying polyimide film is selectively etched by making use of this resist pattern as an etching mask thereby to form a polyimide passivation film or interlayer insulating film having a prescribed pattern.
However, the aforementioned method of forming a polyimide pattern requires two independent steps, i.e. a step of forming a polyimide film and a step of the PEP, making the method troublesome to carry out.
With a view to solve the aforementioned drawback in carrying out the method, a method of patterning a polyimide film without employing the PEP has been demanded. In response to such a demand, a resin composition comprising a polyimide precursor has been proposed.
For example, Japanese Patent Unexamined Publication S/49-115541 discloses a polyamic ester which can be obtained through a reaction between a diamino compound and tetra-carboxylic diester dichloride. Namely, according to this prior art, instead of using tetra-carboxylic dianhydride which is commonly employed in the synthesis of polyamic acid or a polyimide precursor, tetra-carboxylic diester dichloride wherein a photopolymerizable group is introduced through an ester linkage is employed. This polyamic ester exhibits a photosensitivity of negative type so that an exposed portion irradiated with light is insolubilized against a developing solution. Therefore, it is possible to carry out a patterning in the course of forming a polyimide film without requiring the step of the conventional PEP whereby to obtain a patterned polyimide film.
However, not only the process of synthesizing tetra-carboxylic diester dichloride having a photo-polymerizable group, which is a raw material for the polyamic ester, but also the process of synthesizing the polyamic ester are very complicated. Moreover, the end resin product to be obtained unavoidably takes up chlorine ions as an impurity. Additionally, since an organic solvent is employed as a developing solution in the process of developing a polyamic ester film, a large amount of organic solvent is required in the manufacturing line, which is undesirable in viewpoints of safety, sanitation and environment. Furthermore, a swelling of the polyimide film pattern to be obtained may be caused due to the development with an organic solvent, thereby deteriorating the resolution of pattern.
Further, Japanese Patent Publication S/59-52822 discloses, as a photosensitive resin composition of negative type as in the case of aforementioned prior art, a heat resistant photosensitive material containing a compound which has a carbon-carbon double bond and amino group and is dimerizable or polymerizable by an actinic radiation. However, this photosensitive material is defective in that, when it is employed as a passivation film for a resin-encapsulated semiconductor device, it is poor in adhesivity to a semiconductor substrate, to a passivation film formed of an inorganic material for protecting the surface of substrate, or to a sealing resin. Therefore, the employment of this photosensitive material may invite a problem that the reliability of semiconductor device to be obtained would be deteriorated. Additionally, this photosensitive material requires as in the case of the aforementioned polyamic ester the employment of an organic solvent as a developing solution, which is undesirable in viewpoint of safety.
Further, Japanese Patent Unexamined Publication S/60-6365 discloses a photosensitive resin composition wherein an (N,N-dialkylamino)alkyl methacrylate is attached as a salt to the carboxylic group of polyamic acid. However, this photosensitive resin composition is defective in that the solubility thereof to a solvent to be used is poor.
On the other hand, Japanese Patent Unexamined Publication S/62-145240 discloses a polymer having an isoimide structure. This polymer is of positive type photosensitivity wherein, contrary to the aforementioned composition, the exposed portion irradiated with light is made soluble to a developing agent. Since this polymer is of positive type photosensitivity, this polymer can be developed with an alkaline developing solution. However, this polymer is defective in that it is poor in heat resistance and in photosensitivity, so that it cannot be satisfactorily employed as a passivation film in a semiconductor device.
There are known other examples of a photosensitive resin composition exhibiting a positive type photosensitivity as mentioned above. For example, Japanese Patent Unexamined Publication S/64-60630 discloses a composition comprising a solvent-soluble polyimide that can be synthesized through a reaction between a diamine compound having a hydroxy group-substituted aromatic ring and an acid anhydride, to which an o-quinone diazide compound is added as a photosensitive agent. Japanese Patent Unexamined Publications S/52-13315 and S/62-135824 disclose a similar photosensitive resin composition comprising quinone diazide as a photosensitive agent. Japanese Patent Unexamined Publication S/60-37550 discloses a photosensitive resin composition comprising o-nitrobenzyl ester group as a photosensitive agent.
Since these photosensitive resin compositions are capable of being developed with an alkaline developing solution, any problems accompanying with the employment of an organic solvent as in the case of the aforementioned negative type photosensitive resin compositions can be overcome. However, these photosensitive resin compositions are defective in that a difference in solubility to an alkaline developing solution between a light-exposed portion and a light-unexposed portion is not large enough so that it is difficult to form a fine pattern with high resolution. Furthermore, since a polymer constituting a main component of these resin compositions is structurally restricted, the adhesivity thereof to a silicon wafer, a glass substrate, a ceramic substrate, a sealing resin and a metal which are usually employed in various semiconductor devices is poor.
As mentioned above, although the polyimide resin is excellent in electric properties, radiation resistance and heat resistance thus making it suitable for use as a passivation film or as an interlayer insulating film for a semiconductor device, no one has succeeded up to date to develop a photosensitive resin composition which enables to obtain a fine polyimide film pattern exhibiting an excellent adhesion to a substrate by way of a safe and simple manufacturing process.